The president is expected to pick Gina McCarthy to head EPA.

That’s the mindset of Senate Democratic leaders, led by Environment and Public Works Committee Chairwoman Barbara Boxer of California, as they prepare for an intensifying battle with Republicans over President Obama’s climate-change rules.

“My No. 1 job is to make sure that nobody does any harm to the existing Clean Air Act,” Boxer told National Journal Daily on Wednesday in a phone interview from Los Angeles. “No. 2, I have to make sure we have a strong person at the EPA.”

Obama is expected to nominate Gina McCarthy, the Environmental Protection Agency’s assistant administrator for air and radiation, as EPA administrator. “She’s a wonderful person,” said Boxer, whose committee will conduct the confirmation hearing for Obama’s nominee. “She’s really good.”

Boxer has spent the better part of the six years she has chaired Environment and Public Works trying to play offense in the climate debate. Despite her influential perch, Boxer has not come close to passing a big climate bill.

She was pushed aside in 2010 when former Sens. John Kerry, D-Mass., and Joe Lieberman, ID-Conn., and current Sen. Lindsey Graham, R-S.C., tried to muster enough support for a cap-and-trade bill. They ultimately failed too, but they came closer to the legislative finish line than Boxer. In his State of the Union address last week, Obama praised the bipartisan climate bill sponsored by Lieberman and Sen. John McCain, R-Ariz., in 2003. He didn’t mention Boxer.

The Senate landscape has since shifted. Kerry is secretary of State, Lieberman has retired. And Graham and McCain won’t touch climate-change legislation with a 10-foot pole.

That puts Boxer in the driver’s seat of the Democrats’ messaging on climate policy just as Obama, in his speech last week, enunciated more clearly than ever that he intends to move forward with his executive powers to combat global warming unless Congress acts, which is unlikely. He didn’t mention EPA by name, but it’s no secret that’s what he means.

To complement her defense of EPA rules, Boxer is also pushing cap-and-trade legislation with Sen. Bernie Sanders, I-Vt. She declines to admit the obvious: That the measure is dead on arrival in the GOP-controlled House and even faces grim prospects of seeing the light of day on the Democratic-controlled Senate floor. She insists the legislation serves a purpose nonetheless.

“You want to have a bill out there that people can rally around, and eventually to put a huge amount of pressure on people in the Congress,” Boxer said.

Boxer, who has won handily all four times she has run for the Senate, is filling a role many others in her party would find politically precarious. Republicans and even some Democrats find Boxer a polarizing figure on climate change and thus an ineffective legislator on the issue. It’s that very quality that makes her an effective political messenger defending the administration’s actions. Moderate Democrats and those hailing from energy-intensive states up for reelection in 2014 can stay on the sidelines and out of the fight while Boxer plays defense for them.

To be sure, other Democrats will help defend EPA behind the scenes.

The new chair of the Senate Appropriations Committee, Barbara Mikulski, D-Md., will be an important ally as Republicans seek to attach legislative “riders” to spending bills that would restrict funding for climate-change programs. “She’s very dedicated to this issue,” Boxer said of Mikulski.

Mikulski’s voting record over the last few years reflects a reliable vote in support of EPA’s authority over climate change. But when asked about the new chairwoman’s plans to defend the agency in the appropriations process, spokesman Rob Blumenthal referred National Journal Daily to Sen. Jack Reed, D-R.I., chairman of the Appropriations subcommittee that oversees the EPA budget. “Right now we’re focused on finding a solution to the sequester and the rest of 2013,” Reed spokesman Chip Unruh said in an e-mail.

In other words, they don’t want to be bothered as they stay in the background of a fight Boxer is more than happy to wage on their behalf.

The past has shown the easiest way to prevent Republicans—along with a few Democrats—from attaching riders defunding EPA’s climate rules: Don’t pass an EPA appropriations bill at all, and instead fund the agency through a string of continuing resolutions. The Senate hasn’t passed a stand-alone appropriations bill funding EPA since September 2009.

“I stopped riders on the last appropriations bill, and we’ve been able to stop every single repeal they have brought over from the House,” Boxer said.

Coordination between Boxer and Senate Majority Leader Harry Reid will also be critical if and when Republicans seek to nullify EPA’s climate rules through the Congressional Review Act, which requires a simple majority to pass.

In April 2011, the Senate voted on four measures that each, to varying degrees, restricted EPA’s authority. None of them mustered the necessary 60 votes to end debate, but the GOP-sponsored measure nixing the rules altogether received 50 yea votes.

That’s a cautionary tale for Democratic leadership if the Senate faces another round of similar votes this Congress. Under the arcane rules of the CRA, Republicans are just one vote away from nullifying EPA’s power over global warming, and beating Boxer’s defense.

This article appeared in the Thursday, February 21, 2013 edition of National Journal Daily.